Who's got an LED flasher module?

[Lil Abner]

Who's got an LED flasher module? I purchased one on eBay a while back, and finally got around to installing it. When I hit my turn signal, the lights stay ON for about 3/4 second, then starts to flash. The stock module flashes instantly. Anyone else have this problem? Currently the turn signals bulbs are stock, there are no modifications to the turn signal circuit, and this happens for the left turn, right turn, and hazards.

[CrankyOldMan]

I think that a schematic of the module would be helpful. My intial thought is that it's just a relay with a flip-flop (bi-stable multivibrator, a.k.a. 555 timer circuit), and that the outputs may be reversed. If that were indeed the case, then the circuit would have to charge the capacitor first before the circuit would begin to flip-flop, possibly incurring the delay you're seeing. Please keep in mind that I have no idea what the actual module is made up of, and I've only had basic circuits at school. Perhaps CTScott could help troubleshoot this?

[sickpuppy1]

Well if its designed for LED and you still have the stock bulbs in there, that seems to be the issue. Dont use the LED Flasher until you actually put LED's in? The current draw and resistance of the two types of bulbs are totally different.

[Lil Abner]

Ok, I guess I should be more specific. It's a replacement flasher module for our cars. Here's an example listing for the one I got:

http://cgi.ebay.com/ebaymotors/8-Pin...Q5fAccessories

You're suppose to just swap out the existing flasher for this one. It says it's rated at 150W, so stock bulbs shouldn't be a problem. I even tried unplugging half the bulbs, and it still did the same thing. These LED flashers don't rely on current draw/resistance of the bulbs inline.

CrankyOldMan, I did open-up the stock and aftermarket modules. The stock unit is a basic 8-pin 555 timer tied to 2 output relays. The aftermarket appears to be a 16-pin 555/556 timer, also with output relays. Everything but the relays is surface mount, so it's a pain to go back and see the circuit.

In my experience, a poorly designed 555 timer circuit will have a delay when first powered on. Hence the reason I wanted to see if other people have experience with them. Worse case, I'll just get load resistors...

[Betrivent]

Kind of on topic, but I drive large vehicles for a living right now, and some of them are equipped with LED turn signals. Same thing, signal stays on for half a second and then starts flashing. Maybe it's just how some modules are designed?

Also: 8 dollars seems kind of too cheap.

[CrankyOldMan]

My next thought was going in the direction of LED vs. incandescent bulbs, but that doesn't seem to be a factor. Would the impedance of the bulbs affect the timing of the 555? The resistivity of the filament is partly based on temperature, which is itself based on the voltage. Could it be that the cold filaments have a lower resistivity and somehow screw with the timing?

I think that it may also be related to betrivent's comment: I'd wager that the indicator bulb in your gage cluster is still incandescent and also wired into the relay, possibly inducing the same effect. Man, now I want to get out a breadboard and a scope and really dig into this mess. I'm stuck at work all day, and I don't have a scope at home. Perhaps this fall at school I can tinker with the concept.

[Lil Abner]

CrankyOldMan, I went over the circuit, and the 555 timer circuit is not connected to the bulbs like they are in OEM applications. The bulbs are only tied into the relays. The only thing I might have to do is reverse engineer the timer circuit, and see if I can speed it up. I don't know if the size of the charge/discharge capacitor is a factor for this or not. I have some software that I can model it and test it, as well as plenty of circuits on my bench to try.

Betrivent, thanks for the info. But I was sort of hoping you wouldn't say that I will sometimes hit my signals for 2 pulses as I switch lanes, so that delay kills that.

I can get 4 load resistors for $12 from my electronics supplier, so I might plan on using that for now. Then maybe I might have to design my own flasher module, or a fix for the eBay one. Unless someone knows a RELIABLE place to buy another.

So far thanks for all the replies. But I'm still looking for an answer

[Lil Abner]

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